Over the last several years our group and others produces and characterized transgenic mice, that synthesize Hb S or other polymerizing hemoglobin variants as animal models of sickle cell disease. However, none of the mice are ideal models of sickle cell disease. owing to the persistence of mouse hemoglobins or the synthesis of variants which have different properties from those of authentic Hb S. Recent success in application of gene-knockout technology has generate mice that synthesize human sickle and fetal hemoglobins exclusively. The transgenic Hb S-F mice to be anemic with reticulocytosis and 10% irreversibly sickled cells. Preliminary results show the Hb S-F mice to be anemic with reticulocytosis and 10% irreversibly sickled cells. Our overall goal is to use the Hb S-F mice to examine pathologic changes and evaluate therapeutic agents in vivo. Our first specific aim is to characterize the Hb S-F mice over time. We will examine structural and functional aspects of all major organ systems and hematological parameters under ambient conditions to establish baseline data for comparison with experimental interventions of hypoxic stress or treatment with therapeutic agents. Our second specific aim is to use these mice to study the mechanism of initiation of vaso-occlusion. As a new tool to study such mechanisms we will determine the percentage of partially oxygenated sickled cells (POSC), a new type of sickled cells found in the circulating blood of patients as recently described by the applicants. Since POSC contain various amounts of Hb S fibers and undergo sickling without a delay time upon exposure to hypoxia they may contribute to the initiation of vaso-occlusive crises. We will determine the percentage and morphologic changes of POSC in venous and arterial blood before, during and after exposure of Hb S-F mice to various levels of hypoxia. Our third specific aim is to study the affect of Hb F-inducing agents, such as hydroxyurea, butyrate, or erythropoietin, on the percentage of Hb F and F cells using Hb S-F mice. Our fourth specific aim is to evaluate the combined use of hydroxyurea and other agents using the Hb S-F mice. Since the new Hb S-F mice produce human gamma-globin they present a unique opportunity to evaluate the combined effects of therapeutic agents that induce gamma-globin synthesis and agents that inhibit Hb S polymerization by other mechanisms.